DESCRIPTION (Investigator's Abstract): The broad, long term objective of the proposed research is the development of Photodynamic Therapy (PDT) for application in the clinical management of patients with hypervascular cutaneous anomalies, such as port wine stain (PWS). One goal is to investigate the basic mechanism(s) of PDT action on blood vessels buried deep within the skin. A second goal is the development of a more effective and safer method of treatment of patients with hypervascular cutaneous anomalies. The preceding goals will be accomplished in a basic research laboratory and should yield information pertinent to the practical application of the technique to patients. Basic science studies to investigate the fundamental mechanism(s) of PDT action on blood vessels are proposed at three levels: (1) cell culture using human dermal microvascular endothelial cells (MEC); (2) chick chorioallantoic membrane (CAM) model; and (3) chicken comb animal model. PDT is expected to have decided advantages over current therapy because the mechanism of action is photochemical, as opposed to photothermal. Due to the absence of heat production, risks inherent with conventional laser therapy such as hypertrophic scarring, changes in normal skin pigmentation, atrophy, and induration, would not be expected. Therefore PDT is potentially a more effective and safer approach to the clinical management of patients with PWS and other vasculopathies. In addition, the greater tissue penetrance of the longer red wavelengths used in PDT makes it potentially ideal for treatment of deeper, larger PWS malformations, thus substantially expanding the population of patients expected to benefit from laser treatment. Currently only a small population of patients obtain 100 percent fading of their PWS even after undergoing multiple treatments, due to the shallow penetration of light at the wavelengths employed in conventional laser therapy.